Early Rain Covenant Church, based in southwestern Sichuan province, is one of China's unregistered "house" or "underground" churches that some Christians choose to worship at instead of state-sanctioned ones regulated by the government.

On Sunday, dozens of police and government officials raided a gathering in the city of Jiangyou, according to a church statement shared Monday to its Telegram channel.

More than 30 members were taken to a local detention centre for questioning before most were released Sunday night, the church said.

However, two church elders, Wu Wuqing and Yan Hong, were given 15 and 14 days respectively of "administrative detention", rights group ChinaAid told AFP on Tuesday, citing family members.

Relatives have not received any "formal notice on charges", added Bob Fu, the founder of the US-based group.

China's ruling Communist Party has historically regarded organised religion with suspicion, and under President Xi Jinping, has tightened scrutiny of unofficial groups.

Early Rain has drawn the ire of authorities previously. In 2019, its leader Wang Yi was sentenced to nine years in jail for "incitement to subvert state power", drawing condemnation from the United States.

This year, Chinese authorities have interrupted gatherings or detained the leaders of multiple unregistered churches across the country, rights groups say.

Asked about this on Monday, China's foreign ministry defended the country's laws on religion.

"The Chinese government lawfully handles religious affairs and protects citizens' freedom of religious belief and normal religious activities," spokesman Lin Jian told a news briefing.

"We resolutely oppose using so-called religious issues to interfere in China's internal affairs," he said.

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At Early Rain's service on Sunday, police wearing SWAT uniforms surrounded dozens of congregants, including children, footage shared by the church showed.

Authorities, including local police and religious affairs officials, held people who were not taken to the detention centre at the hotel where the gathering had taken place until around 6:00 pm, the church said in its statement.

It is not the first time this year Early Rain has come into conflict with the authorities.

In January, the church said nine of its members, including senior leaders, had been detained in a "concerted operation", with two others unaccounted for.

The same week, Yayang church in eastern Zhejiang province was scaffolded and had its cross removed, AFP reporters saw, before it was demolished in May, according to ChinaAid.

Last October the United States condemned the detention of almost 30 leaders of another prominent underground church, Zion Church.

In May, Zion said 18 people were still being held.

Following a visit to Beijing in May, US President Donald Trump told reporters he had brought up the Zion case with Xi during talks, and said the Chinese leader would "strongly consider" the release of its pastor.